An apparatus for combining numerous liquid streams to form a multilayered liquid stream is used as a means for efficiently producing a film having a multilayer structure.
As particular example, a multilayer co-extrusion feed block is known (see Patent Documents 1 to 3 described later). Furthermore, so-called an interfacial surface forming apparatus (ISG: Interfacial Surface Generator), i.e., a square mixer is also known (see Patent Documents 4 and 5 described later).
However, the apparatuses proposed in the Patent Documents 1 to 3 can practically produce only a multilayered film comprising up to 300 or less in the total number of layers. If such an apparatus is going to be used to produce a multilayered film comprising more layers, the apparatus must be enlarged in one direction. As a result, stagnant liquid regions are formed in the apparatus. The liquids retained in the apparatus thermally deteriorate and generate foreign matters. In an extreme case, there occurs such a phenomenon that the liquids do not flow uniformly in the apparatus.
In the apparatuses proposed in the Patent Documents 4 and 5, a multilayer co-extrusion feed block and a square mixer are combined to allow the number of layers to be increased efficiently. However, in the case where a multilayered film requiring very high layer accuracy such as an optical interference film or a refractive index control film is produced, the passages of liquid streams in the mixer are deformed to cause layer deformation. So, for maintaining high layer accuracy, the upper limit in the number of layers has been 700 or less. In addition, a multilayered film complicated in the constitution of layer thicknesses required as a refractive index control film or the like could not be produced by any of these conventional methods or apparatuses.                Patent document 1: U.S. Pat. No. 3,884,606        Patent document 2: U.S. Pat. No. 3,687,589        Patent document 3: JP 2003-112355 A (page 2 )        Patent document 4: U.S. Pat. No. 3,565,985        Patent document 5: JP 3,264,958 (page 2 )        